The present invention relates to a method of manufacturing semiconductor device, and more particularly to a method of manufacturing a semiconductor device by forming a silicon oxide film and a PSG film, a BSG film, or a BPSG film and the like by mixing organic silane and ozone, or gas containing an impurity such as phosphorus or boron.
The inventors of the present application had previously found that a SiO.sub.2 film formed by a TEOS-O.sub.3 reaction has advantages such as excellent step coverage and that very few articles are generated during film formation. The present inventors had also found that characteristics of the film depend on the O.sub.3 concentration, and that the following advantages are obtainable as the O.sub.3 concentration gets higher.
(1) Increase of film forming speed PA1 (2) Increase of film density PA1 (3) Reduction of etching rate PA1 (4) Reduction of leakage current PA1 (5) Reduction of --OH, H.sub.2 O components in the film PA1 (6) Improvement of crack resistance PA1 (7) Reduction of stress PA1 (8) Improvement of step coverage (Flow configuration) PA1 Al-BPSG, PSG, thermal SiO.sub.2 PA1 W-BPSG, PSG, thermal SiO.sub.2 PA1 WSi.sub.x -BPSG, PSG, thermal SiO.sub.2 PA1 Al-BPSG, PSG, thermal SiO.sub.2 PA1 Poly-Si-BPSG, PSG, thermal SiO.sub.2
On the other hand, however, the TEOS-O.sub.3 reaction being a surface reaction, the reaction is very sensitive to the substrate surface on which the film is formed, and the characteristics of formed films sometimes differ when substrate films are different.
FIGS. 7(a), 7(b) and 7(c) show a method of forming a CVD-SiO.sub.2 film by a Tetra-Ethyl-Ortho-Silicate (TEOS, Si(OC.sub.2 H.sub.5).sub.4)--O.sub.3 reaction according to a conventional technique.
In FIG. 7(a), reference numeral 4 denotes a thermal SiO.sub.2 film formed on a surface of a Si substrate 2, and 6 denotes a polycrystalline silicon film (hereinafter referred to in brief as a "poly-Si film") formed on the thermal SiO.sub.2 film 4. Examples of semiconductor devices having such a structure include a MOS transistor comprising the thermal SiO.sub.2 film 4 as a gate SiO.sub.2 film and the poly-Si film 6 as a gate electrode.
Next, a CVD-SiO.sub.2 film 8 is formed as an interlayer insulating film by the TEOS-O.sub.3 reaction as shown in FIG. 7(b).
It has now been found that the surface of the CVD-SiO.sub.2 film formed by the TEOS-O.sub.3 reaction is even (see partially enlarged view A) where the backing is the poly-Si film 6 as shown in a perspective view of FIG. 7(c), but that unevenness is sometimes produced on the film surface (see a partially enlarged view B) when the backing is a thermal SiO.sub.2 film 4.
FIG. 8 is a diagram showing measurements of unevenness of the surface of the CVD-SiO.sub.2 film formed using such a conventional method by the present inventors. In FIG. 8, the abscissa shows ozone concentration (%), the ordinate shows the difference in unevenness on the surface of the CVD-SiO.sub.2 film (.ANG.), for two different backings (thermal SiO.sub.2 film and Si film). In such a manner, an even CVD-SiO.sub.2 film surface is obtainable regardless of the O.sub.3 concentration when the backing is Si, but the smoothness of the film surface is dependent upon the O.sub.3 concentration when the backing is a thermal SiO.sub.2 film, and there is the tendency that the unevenness of the CVD-SiO.sub.2 film surface becomes greater as the O.sub.3 concentration gets higher.
The unevenness was measured by applying a probe to the surface of the SiO.sub.2 film and measuring the distance of vertical movement thereof.
FIG. 9 is a diagram showing the results of measurement of formation rate of the CVD-SiO.sub.2 film, formed by using the same conventional method as that used in FIG. 8. As shown in the Figure, control is easy in manufacturing since dependency of the formation rate on the O.sub.3 concentration is small when the O.sub.3 concentration reaches approximately 1% or more, where the backing is of Si, but the formation rate depends greatly on the O.sub.3 concentration when the backing is a SiO.sub.2 film, and the formation rate is lowered as the O.sub.3 concentration gets higher. Thus, there is the problem in manufacturing of control of film thickness.
When the O.sub.3 concentration is lowered (to approximately 3% or lower), the film quality of the CVD-SiO.sub.2 film is not sufficient, and the step coverage at a step portion changes from a flow configuration to an isotropy, which, therefore, presents difficulty when the CVD-SiO.sub.2 film is used as an interlayer insulating film.
As described above, a conventional method presents a dilemma that the film quality is good but subject to serious influence by the backing when the O.sub.3 concentration is high. On the other hand, however, the film quality is less affected by the backing but the film quality is diminished when the O.sub.3 concentration is low. Thus, it is difficult to solve all the problems at the same time by use of a specific O.sub.3 concentration.